The new fuel for us all is veg oil
I have heard that in certain parts of the UK, there is already a thriving trade in used fish & chip shop, deep frying oil, with a few additives to make diesel cars run on it.
It is apparently illegal to use this, unless you pay over the duty & VAT to Customs & Excise.
Police & C & E, are therefore stopping all cars, with exhausts that smell strongly of FISH